add lifecycle callback struct for client and server rpc connection management

[emaxerrno]

struct connection_callbacks {
    void connection_open(const ...&);
    void connection_error(const ...&);
    void connection_exception(const ...&);
    void will_parse_header();
    void did_parse_header(const &)....
    void will_parse_body()
    void did_parse_body(const &...)
    void connection_set_error()...
    void connection_disable....
    void connection flushing
   void connection_close
};